1. Field of the Invention
This invention relates to surface state inspection apparatus, and more particularly, to surface state inspection apparatus which is suitable for detecting foreign particles, such as opaque dust or the like, other than a circuit pattern, adhered to a substrate, such as a reticle, a photomask or the like, or for detecting color centers in a reticles, in the semiconductor production process using a deep-ultraviolet-light exposure method.
2. Description of the Prior Art
In the IC (integrated circuit) production process, in general, an IC is produced by transferring a circuit pattern for exposure formed on a substrate, such as a reticle, a photomask or the like, to the surface of a wafer coated with a resist using a semiconductor printing apparatus (a stepper or a mask aligner).
At this time, if a foreign particle, such as dust or the like, is present on the surface of the substrate, the foreign particle is also transferred in the transfer operation, causing a decrease in the yield of the IC production.
Particularly when a circuit pattern is repeatedly printed on the surface of a wafer by a step-and-repeat method using a reticle, one foreign particle on the surface of the reticle is printed on the entire surface of the wafer, causing a large decrease in the yield of the IC production.
Accordingly, it is indispensable to inspect for the presence of foreign particles on a substrate in the IC production process, and various kinds of inspection methods have been proposed. Particularly, inventions have been disposed closed in U.S. Pat. No. 4,800,282 (which corresponds to Japanese Patent Application Public Disclosure (Kokai) No. 61-182238 (1986)) and Japanese Patent Application Public Disclosure (Kokai) No. 61-222145 (1986)). According to these inventions, an ultraviolet beam is merely projected or projected while being scanned onto the surface of a wafer or a semiconductor substrate to detect fluorescence issued from a foreign particle remaining on the surface of the wafer or substrate.
However, two kinds of apparatus described in the above-described publications have the following disadvantages: a first apparatus for detecting the presence of a remaining photoresist, serving as foreign particles, on a wafer only detects fluorescence generated when the wafer is merely irradiated by light only with a single detector, the position of the remaining photoresist cannot not identified. If a foreign particle is detected by a spot scanning method, that is, by scanning the wafer with a beam, as in a second apparatus, the position of the foreign particle can be identified in principle. However, the position of the foreign particle moves in some cases on a reticle in the course of inspection. Accordingly, even if, for example, only one foreign matter is present on the reticle, the apparatus misdetects as if a plurality of foreign particles were present on the reticle if the movement of the foreign particle occurs several times in the course of inspection.